Method of making magnetic structures



106. COMPOSITIONS, 4 CRGSS ,RZFERENCE I Examiner COATING 0R PLAS'HC Feb. 16, 1932'. R. GILLIS 5,1

METHOD OF MAKING MAGNETIC STRUCTURES Filed Nov. 8, ,1928

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- PM cmr xv/c/ngz mama Febri e, 1932 phonic communicating teresislossthan 3- sired shape and treated to give Other features and advantages of-the in-" I reduced to a finely divided form or manner, as for example, in a the v a complete loading coil core, and

compositions o limited to the UNITED STATES} PATENT-T OFFICE nan-nan. exams. or an email, rumors, v rerun moonronann, or new relax, :a.

assr'enon 'ro wnsrmm nnncrnrc com 1., a oonrona'rron or saw your union or me nennrrc srnucrunns Appllcatlon. fled Iovember a, ices. sum :6. 311m efiective resistanceof an'inductance coil hav- This invention relates to a method of making mag tic structures, and more particularlytoamethod of produ magnetic cores of a compressed 'dust type or use in telesystems.

The object of the invention is to provide a method of reducing magnetic structures having stab e magnetic properties under varying magnetic'conditions.

10 One embodiment of the invention contem-.

lates the construction of magnetic cores for oading coils of nickel-iron alloys in finely I divided form having higher inherent magnetic permeabilityand lower inherent hys- 4 iron. ,These properties are obtained by treating metal or alloy particles with fiscalmsula' an ting coating they are compressed into size. The cores'are then heat substantially zero stability oi permeability and hysteresis loss to magnetization as determined by the composition of the alloy.

vention will become apparent from the following detailed description ofone' embodiment thereof, reference being hadto thelaccompanyin drawings, wherein Fig. 1 ustrates a plurality of magnetic rings or core parts made in accordance with present invention and combined to form Fig. 2 shows a curve illustrating the optimum annea tem ratures for various nicke -ir0n alloys to procure bstantially zero stability of permeability ization." v

It will be' understood, however, that Fig, 1 is merely illustrative and the invention is not productionof this form of core, but is adapted to the productionof magnetic parts of various forms.

By the term zero stability of permeability and hysteresis loss'to instantaneous magnetization, as employed in the specification and in the annexed claims, permeability and hysteresis loss of the mate rial, and consequently the inductance and ting material t9 form thereonafter which cores of the deasfull is meant that the centages of nickel and iron. These alloys described in the patent are prepared as fully to O. P. Beath and H; M. E. Heinicke, 1,669,649 issued May 15, 1923. a

An alloy thus prepared isrolled while hot into relatively thm slabs and quenched on a to produce a fine crystalline structure which' 'is very desirable since the distinteg'ration of the material takes place at the crystal boundaries, and consequently the smaller the' size of the crystals, the finer the dust which'can be produced from thefinished product. The magnetic alloy thus received in slab form is any. wellknown a hammer mill or other suitable reducing apparatus and subsequently pulverized in" an attrition mill.

eve is placed'in a closed container and an-. nealed at a temperature of approximately 885 C. The annealed dust is removed from .The dust from the mach-mm is sifted,- and the portion passing through 'a 1 20 dust, in.

the containerm the form. of a cake which is again reduced to "a powder by crushing rotary crusher and subsequently grindmgin an attrition mill. The grounddustjs agam sifted through a. standard 120 mesh screen and the dust passing through such a screen isinsulated with a lution of chromic acid, sodium silicate, pow%red talcum and water-'1 mm eated and stirred until (E3 described in Patent No. 1,669,643 issued y 15, 1928, toJ. W. Andrews and R. Gillis. As clearlydescribed therein,'the desired permeabili can be obtained by varying the amount 0 ,the insulating material.

Obviously, other methods of insulating the dust well.- known .tothe art, could also be em loyed. w

The insulated dust is sifted through a 16 mesh screen and-placed in a mold and compressed into core parts' under a pressure of approximately 200,000 pounds per square inch. The core parts are then transferred in.

air tight containers to an .annealing furnace where they are annealed at an optimum temperature determined bythe composition of the alloy comprising the dust. As indicated by the graphical representation of Fig. 2,,fer-

rous alloys having various'percentages of sy nickel maybe heat treated "at these optimum tom eratures so that the magnetic structures pro uced therefrom will' have substantially zero stability of permeability and hysteresis loss to magnetization. 'f .f 5

The law deducible from the curve (if-Fig.

2 0 2 is that the annealing temperature necessary to produce a satisfactory-stability of permeability and hysteresis loss must, be -in'-' creased as the percentage .of nickel '"in the" alloy is decreased. In other words, the an- 2 7 nealing temperature should be selected in accordance with the'formula represented graphically by'the curve,whichis:" I

' .382 NH-50N- 1056 v 3 Where T is the annealing temperature degrees centigrade and N is the percent of nickel in the alloy. Stability of permeability and hysteresis loss are very desirable inthe construction'of inductance coils for the inductive loading of telephone circuits. Improved transmission characteristics are obtained when inductance coils are used having substantially constant inductance and a low and constant effective resistance. The constancy ofsuch coils cannot be economically obtained except by the use of stable core material. 'The core material can only be made stable by the optimum choice of composition and heat treatment. A heat treatment of the cores at app'roximatelv 500 C. has been found to have a very desirable efiect upon .the hysteresis loss. In order to take advantage of such aheat treatment it is-necessary to choose an alloy having the-proper nickel .t 'content so that satisfactory's'tability'as well as low hysteresis. loss are obtained simul- "taneously. The very high quality of the magnetic material is' therefore obtained'by the optimum choice of composition and heat treatment-as illustrated bythe-c'arjve of Fig. 2; In order to make the core chemically stable and to remove all soluble substances such as chromates, the core arts are boiled in water until a solution obtained,'bv boiling a crushed test in water, will show only .a small "traoeo soluble'chromates whentested with silver nitrate. Following the washing, the core parts are placed in adryingtank where theyare heated and'the -tankevacuated to ture containin 74% nickel into a predetermined c1e,which com insulated partic es of a nicke -,iron alloy into 9 .nickel in the alloy.

ture selec 1grees centigrade and L thoroughly dry @9 was PW. is;

cle which consists in compressing finely divi ed particles of a ferrous magnetic alloy shape, an heat treating the resulting article at a temperatureof approximately 550 cenitigrade to give stable magnetic properties under'varym magnetic conditions.

, 2. The met 0d of making a magnetic arti- 'rises formin finely divided a predetermined shape b pressure, and annealin the formed artic e at a temperature selecte in accordance with the formula T as2 N= F5oN+1056 where T the annealin tem erature indegrees centlgrade and is t e percent of .3. The method of making a magnetic core which comprises formin finely divided par- 1 ticles of a nickel-iron a oy into a predetermined shape. under a pressure of approximately 200,000 pounds per square inch,', and heat 212813;? the' formed core at a temperain accordance with-thejormula v 1"-= .382 N*+50N'1056 where .T is the annea temperature in de f is the 'percentof nickel in the alloy.

. The f making a ma netic core, ampu e pp g i is p to finely divided particles of a nickel-iron alloy toforni them into "an annular shape,

-. 1d the'formedarticle at a tem- 115. perature g selected in accordance with :the

ormulais the percent of where is the temperatur e 'in de- 6 1 I: gr .s centigrade and j nickel in the In witness whereof, I hereunto subscribe my natn this 27th da ofOctober' A." D: 1928.

al winding is applied, 

